1. Field of the Invention
The present invention relates generally to sheet metal forming, and more particularly to a method and apparatus for designing the manufacturing process for making sheet metal parts.
2. Description of the Related Art
The task of designing the manufacturing process for making sheet metal parts can be very time consuming and expensive. The tooling design is typically decomposed into a number of operations and die shapes needed to produce the desired part. In parallel, the manufacturing process parameters, such as the initial shape of the blank, the blankholder force, and the shape of the drawbeads are also defined. Additionally, the design cycle must account for a number of potential defects, such as tearing of the sheet metal, excessive thinning or thickening of the part, insufficient flange remaining following the forming operation, and incorrect final part shape.
Fortunately, the time and expense incurred in designing the manufacturing process can be significantly reduced by accurately simulating the forming processes before committing to hard tooling. For example, a simulation program know as ABAQUS has been developed by Hibbit, Karlsson and Sorensen, Inc. of Pawtucket, R.I. to model deformation processes and predict some sheet metal forming defects such as tearing and springback. The outcome of a simulation performed using ABAQUS can be used to select the forming parameters and design the die shapes of a forming process.
However, ABAQUS has some significant drawbacks. For example, in the xe2x80x9cExplicitxe2x80x9d version which utilizes explicit integration, the forming tools for 3-dimensional analysis are defined by a finite element mesh. The construction of such a mesh for the forming tools is usually very time consuming in terms of both human and computer resources. In addition, the finite element mesh involves approximating the actual shape of the tools as a mesh of triangular facets or bilinear four-node elements, which compromises the accuracy of the results.
ABAQUS also has a xe2x80x9cstandard/implicitxe2x80x9d version which utilizes implicit integration and which allows the user to input the shape of the forming tools as either a finite element mesh or an exact mathematical model. However, the exact mathematical model must be in a unique ABAQUS format, which is typically very time consuming to construct.
Anther shortcoming of ABAQUS relates to the effort required to model drawbeads. In the case that drawbeads are used, the only direct way of implementing them into the model is by a complete representation of their detailed geometry as part of a large three-dimensional tool, thereby increasing the amount of human and computer resources required to conduct the analysis.
It would be desirable, therefore, to have a method and apparatus for modeling a manufacturing process such as sheet metal forming which provided accurate results by allowing exact mathematical modeling of the forming tools, while reducing the human and computer resources needed to conduct the simulation.
A method of designing a manufacturing process, according to an exemplary embodiment of the invention, comprises the steps of representing a workpiece as a plurality of finite elements, representing a forming tool with a mathematical equation, simulating a deformation of the workpiece by the forming tool with a finite element model, wherein the finite element model is integrated with explicit integration, and adjusting a characteristic of at least one of the workpiece and the forming tool to alter a final shape of the workpiece. The method may be carried out with an apparatus which includes a memory device which stores a program including computer readable instructions and a processor which executes the program instructions in accordance with the method.
After the deformation of the workpiece has been simulated by the finite element model, the characteristics of the workpiece and forming tool can be modified to improve the final shape of the workpiece. For example, the user can modify forming parameters such as the punch travel distance, the blankholder load, the speed of the forming process, and the coefficients of friction for the forming tool. The user can also modify the shape of the workpiece, the shape of the forming tool including drawbeads, and the material of the workpiece, to improve the final shape of the workpiece. After the finite element simulation produces an acceptable final workpiece shape, an actual workpiece can be formed with actual tools based on the simulation.
The invention also relates to an article of manufacture comprising a memory device such as a compact disc containing computer readable program instructions embodied therein for designing a manufacturing process.